After Whatsapp has been try limited of Voice Call feature. Now its official announcement and can be used and availabe for android smartphone base include Nokia X Family.
How to get this feature? we don't need to invite other user which is voice call feature activated. You just need to install the latest update todays. you can get its via Whatsapp official website or Google playstore ( if its has been installed google play service and Play Store.)
How to Install Google play please go to :
how to use it? Well The main menu of WhatsApp is 3 Tab.They are calls, chat and Contact. call tab content is history call log. you may choose contact and tap phone icon to calling.
Make sure both device was installed latest version of Whatsapp for Voice call work 100%. Now adays whatsapp call is available for all Android base include Nokia X platform. For iOS its still releases for some week future. for other platform like BB 10 and WP. untill now not official announcement .